Central Heating Electrical Fault.

[matt1e]

the off terminal on your room stat should not be connected to neutral
also the red should go to common and the yellow to on, swap them around whilst your on
Matt

 

[BlueMoonMole]

the off terminal on your room stat should not be connected to neutral
also the red should go to common and the yellow to on, swap them around whilst your on
Matt

Get a multimeter and test some wires...

Schematics seem ok. Must be a short somewhere...

 

[matt1e]

Get a multimeter and test some wires...

Schematics seem ok. Must be a short somewhere...

No they don't
if the room stat is connected as shown in that schematic then what is happening is that if the hotwater is off or satisfied and the room stat is satisfied then the misposition valve's internal microswitch will place a dead short between line and neutral via the valve and cylinder stat (when it calls for heat)

Live from hotwater on through the cyl stat( termc/term1 ) though the valve orange via microswitch when the valve is fully open
out off valve via white into room stat c terminal
down to neutral via roomstat off term
the neutral needs to be taken out off the stat off or satisfied terminal and connected to neutral or made safe

capiche?
Matt

 

[BlueMoonMole]

Meant to say 'other than above... Schematics are ok. Test some wires with a mulitmeter'

If the RS isn't causing the short; there's a short somewhere else.

But I imagine, as you've mentioned, it may well be that.

 

[twgas]

remove the blue wire to room stat, a digisat only needs common and switch (on your system, anyway).

 

[D_Hailsham]

the off terminal on your room stat should not be connected to neutral.

I agree.

Also the red should go to common and the yellow to on, swap them around whilst your on

That's good practice, but not essential.

Isn't fault finding easier when you have a diagram in front of you.

 

[chadvandonkey]

Sounds like we have all come to the same conclusion at the same time.

The Room stat COMMON is now the Red cable from CH ON terminal 7

The Room stat ON is now Yellow cable from termnal 8

The Room stat Blue cable is connected to N at the Room stat itself (not OFF) Off now has no connection.

Your explanation of a dead short on Call for Water is exactly when it happens so fingers crossed it seems to be working perfect now.

 

[matt1e]

the off terminal on your room stat should not be connected to neutral.

I agree.

Also the red should go to common and the yellow to on, swap them around whilst your on

That's good practice, but not essential.

I agree unless the stat incorperates an anticipator

Isn't fault finding easier when you have a diagram in front of you.

totally agree

fingers crossed it seems to be working perfect now.

I'll be fine, I would think about replacing the cylinder stat for good measure though as the contacts are probably close to knackered now
they are not expensive

Matt

 

[D_Hailsham]

Also the red should go to common and the yellow to on, swap them around whilst your on

That's good practice, but not essential.

I agree unless the stat incorporates an anticipator

I agree; and the OP's stat (Drayton Digistat+) does not have an anticipator.

 

[chadvandonkey]

Guys,

A big thank-you to all of you!!!!!

All seems to be fixed and has run all weekend with no problems - good job considering everything is new or recently new. I have put a new tank stat on now too just in-case.

It was plainly obvious to see the wiring fault with the circuit drawn out - even to me. A picture speaks a thousand words and all that.

Anyways, all sorted now so thanks again.

Stu.

 

[gcrplumbingheating1]

this sounds like a complex fault! i recently attended a a similar fault albeit on a s plan system. in this case the fuse was blowing with a hw demand at first intermitantly then more and more frequent until you couldnt make a demand without the fuse blowing. after basic checks the zone valve,cylinder stat,pump and programmer were ruled out.i then disconnected the switch live cable to the appliance and birdged it out, the boiler would fire every time with no problems, with the switch live feed connected from the wiring centre to the boiler the fuse would blow! turns out the was a short-circuit between switch-live and earth! difficult to spot when it was so intermitant, but more apparant when re-occuring!

 

[Agile]

In short I have had replaced all components in the loop with brand new ones (Room stat, Tank stat, 3 way valve, Programmer, Pump & Brand new Worcester boiler). The boiler was replaced by a Gas Safe Engineer who re-checked all of the wiring and is happy it is wired correctly. After it blew fuses with the new boiler fitted we then tried another 3-way valve and a new programmer and it still blew the fuse.

I have since had an Electrician to look at the cabling in the walls as this seemed the only thing left to check and he Megger tested all the cables and found no cable or insulation faults. He suggested that the fault must be a live to neutral fault as this would blow the fuse and not trip the RCD, whereas a live to earth would trip the RCD.

This was not a complex fault at all, in fact it was a very simple wiring error.

Where the problem went wrong was the blanket assumption that the RGI who checked the wiring had done that properly.

Also the electrician had ( easily ) worked out the nature of the fault but had been unable to identify it.

Now I cannot understand the mindset of an RGI who can check the wiring and say its OK but still be unable to identify the fault. I will leave my thoughts unsaid but its a prime example of when somebody should admit that they are out of their depth.

Tony

 

[D_Hailsham]

this sounds like a complex fault!

That's the impression you might get from just reading the OP's opening post. But if you read on, you will see that it was very simple to resolve.